Mesothelioma occurs when cells of the mesothelial lining of certain organs and cavities begin dividing uncontrollably, resulting in the formation of tumors. These cancer cells may spread to other parts of the body and begin growing new mesothelioma tumors. This spread of mesothelioma is called metastasis.
About Mesothelioma Metastasis
Like in other malignant cancers, the cells of mesothelioma tumors may metastasize. Mesothelioma metastasis occurs when mesothelioma cancer cells break away from the original tumor site and spread to other parts of the body. Malignant mesothelioma cancer cells may be spread through the lymph system or the bloodstream but often first begin infecting the lymph node. They are then transported to distant organs to begin growing new mesothelioma tumors. The more advanced the disease becomes, the farther it spreads. Treating mesothelioma before it spreads is key to increasing life expectancy.
Factors Affecting Mesothelioma Metastasis
A number of factors are involved in mesothelioma metastasis. These may affect the speed at which mesothelioma metastasizes, where the cancer spreads to, and may affect the outcome of treatment.
- Type of Mesothelioma
The specific type of mesothelioma may have an effect on how likely it is that mesothelioma will become a metastatic cancer and may affect where new cancers are likely to grow. Mesothelioma metastasis is more preventable in earlier stages but when not diagnosed until stage III or IV is already considered malignant or metastatic. Mesothelioma is most likely to first metastasize to surrounding organs such as the liver, kidneys or other organs of the chest and abdominal area, while bone and brain metastases are not as common.
- Mesothelioma Cell Type
Mesothelioma cells are identified as one of three types including epithelioid, sarcomatoid or biphasic. Epithelioid mesothelioma cells, similar in appearance to skin cells, are more likely to “stick” to one another and are less likely to metastasize. The tumors formed from sarcomatoid cells are considered to be “disorganized” and more easily become metastatic mesothelioma. Biphasic mesothelioma tumor behavior is difficult to predict and the likelihood of metastasis is dependent upon whether most cells are epithelioid or sarcomatoid.
- Treatment of Metastatic Mesothelioma
As mesothelioma becomes more advanced, it metastasizes further and becomes more difficult to treat. Tumor development on vital organs such as the liver, heart, lungs, kidneys or brain may compromise overall patient health. When mesothelioma has become advanced, the patient may not be able to tolerate aggressive procedures, making treatment more challenging. In advanced cases, treatments may be used to slow the advancement of metastasis.
- Mesothelioma Metastasis and Prognosis
The prognosis of a mesothelioma cases is partly based on metastasis. In most cases, the farther the cancer has spread or metastasized, the poorer the prognosis and shorter the life expectancy. In advanced mesothelioma, treatment options may be limited to slowing the further metastasis of the cancer and increasing the comfort of the patient.
Staging of Metastatic Mesothelioma
Mesothelioma is considered to be an aggressive and malignant cancer because it has a high likelihood of metastasizing to other areas of the body. Metastasis occurs when cancerous tumor cells break off from the original tumor site and spread to other areas of the body through the blood stream or lymph system.
These mesothelioma cancer cells that are deposited on other organs or in distant areas, will begin growing new tumors. The new tumors are comprised of mesothelioma cells of the same type as the original cancer and are still identified as mesothelioma.
Mesothelioma is identified by stages which indicate how advanced the cancer has become. In the later stages of III and IV, mesothelioma has spread beyond the immediate area and has metastasized.
- Stage III – Mesothelioma has spread beyond the original site but is confined to nearby lymph nodes or organs. Pleural mesothelioma may have spread into the chest wall, while peritoneal mesothelioma may have invaded the diaphragm or abdominal muscle.
- Stage IV – Mesothelioma has clearly become metastatic and has spread to other organs, some of which may be far away from the original tumor. It is the most advanced stage of mesothelioma and treatment options may be limited to slowing the further spread and palliative care.
In most types of cancer, the stages are clearly defined by how far or how much the cancer has metastasized. As mesothelioma is so rare, with only about 3,000 new cases emerging each year, a standard system for staging has not been universally adopted. Different physicians may have different criteria for determining the stage of cancer.
Because of the lack of clearly defined staging systems for metastatic mesothelioma and as treatment options may be limited, it is essential that patients diagnosed with mesothelioma seek advice or treatment from a mesothelioma specialist.
Route of Mesothelioma Metastasis
As mesothelioma becomes more advanced, it may metastasize to organs or tissues in the area surrounding the original tumor and may spread to distant organs. This mesothelioma metastasis occurs through the lymph system or through the bloodstream.
The lymph system is considered to be a secondary “circulatory system” is similar to the vascular system but not as organized. Rather than transporting blood cells and serum to carry oxygen and nutrients through a series of clearly defined vessels, the lymph system transports lymph fluid and has lymph “nodes” which function as collection points or filters to trap bacteria and other harmful cells.
Mesothelioma cancer cells may metastasize through the lymph system to other parts of the body but may also become stuck in the lymph nodes. As mesothelioma metastasis advances, cancerous cells are found in greater numbers and in more lymph nodes that are further away from the original tumor site. The location and number of mesothelioma cells identified in lymph nodes is used to determine stage of mesothelioma.
The circulatory or vascular also a potential route for mesothelioma cells to metastasize if they have been able to enter a blood vessel near the tumor site. This method of spread is not easily identified but may result in metastases occurring in distant areas or on organs far away from the original tumor location.
Mesothelioma Metastasis and Angiogenesis
When mesothelioma tumor cells are transported to a new area, a new blood supply must be established in order for a new tumor to grow. The establishment and growth of a new network of blood vessels to supply metastatic mesothelioma tumor cells with oxygen and nutrients is known as “angiogenesis”. If angiogenesis does not occur, it appears that metastatic mesothelioma cells cannot begin new tumors. Angiogenesis inhibitors are medications which prevent the growth of new blood vessels. These medications are one type of “newer” treatment methods that show potential in preventing mesothelioma metastasis and may also help to shrink existing tumors.
Treatment of Metastatic Mesothelioma
As mesothelioma advances, it becomes more challenging to treat. More advanced cases of metastatic mesothelioma may be limited to palliative treatment options which are intended to increase patient comfort. Palliative methods may help to reduce the severity of symptoms or prevent further metastasis but may also help to increase life expectancy.
References:
American Cancer Society, (18 May 2015), What is Mesothelioma?, ACS Cancer.org, Accessed on 20 January 2016 http://www.cancer.org/cancer/malignantmesothelioma/detailedguide/malignant-mesothelioma-malignant-mesothelioma
American Cancer Society, (06 March 2015), What is Metastatic Cancer?, ACS Cancer.org, Accessed on 20 January 2016 http://www.cancer.org/cancer/malignantmesothelioma/detailedguide/malignant-mesothelioma-malignant-mesothelioma
Chari, A., et al, (15 January 2015), Cerebral Metastasis of a Malignant Pleural Mesothelioma, Cureus, Accessed on 20 January 2015 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4494585/
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Mesothelioma Applied Research Foundation, (2013), What is Mesothelioma?, MARF CureMeso.org, Accessed on 20 January 2016 http://www.curemeso.org/site/c.duIWJfNQKiL8G/b.8578801/k.639A/What_is_Mesothelioma.htm
National Cancer Institute, (2016), Malignant Mesothelioma – Health Professional Version, National Institutes of Health, Accessed on 20 January 2016 http://www.cancer.gov/types/mesothelioma/hp
National Cancer Institute, (2016), Angiogenesis Inhibitors, National Institutes of Health, Accessed on 20 January 2016 http://www.cancer.gov/about-cancer/treatment/types/immunotherapy/angiogenesis-inhibitors-fact-sheet
